Interfaces casts are type-checked differently to class casts?

Question

hi,
this is a multipost of
http://forum.java.sun.com/thread.jspa?threadID=677488&tstart=0
as i'm hoping some compiler guys are hanging around in here :)
I'm just wondering why interfaces are type-checked differently to class casts when casting between siblings in the inheritance hierarchy.
e.g. casting a String to an Integer fails, but declaring
interface IString {
   String toUpperCase();
interface IInteger {
   int intValue();
} and casting between IString and IInteger works fine?
any help appreciated,
thanks,
asjf

Answer 1

Unless you have specific memory usage requirements so that you must use arrays, just use a java.util.List:
public abstract class Type<A extends Arg> {
    protected abstract List<A> method();
   // or if the only needs to read it can be more convenient to have
    protected abstract List<? extends A> method2();
public class Sub extends Type<SubArgs> {
    protected List<SubArgs> method() { ... }
    // sub class can be more specific for method2 if it wants to
    protected List<SubArgs> method2() { ... }
}